The present invention is directed to an apparatus for measuring parameters such as the temperature of an energized electric power line. As set forth hereinafter, many parameters such as vibration, strain, temperature, etc., may be measured and signals indicative of such parameters transmitted to a remote location on a real-time basis. However, the present invention was originally conceived and reduced to practice in the environment of measuring the temperature of an electric power line as a vehicle for increasing the thermal capacity of an electric power system. Hence the invention will be described in that environment notwithstanding the many other applications of the present inventive concept. Thus the following explanation of the invention should be understood as merely illustrative and not as a limitation.
The total capability or capacity of an electric power system may be limited by any one or more of the following factors: (a) surge impedance loading or stability constraints; (b) voltage profiles; (c) energy losses; and (d) thermal rating. Most electric power systems consist of relatively short lines and therefore the load capability or capacity is normally limited by the thermal rating. The thermal rating is, of course, the maximum current that the line is capable of carrying and is normally based upon a maximum allowable or safe conductor temperature with an assumption of very pessimistic climatological conditions.
The most predominant parameter or factor utilized in establishing the thermal rating of an overhead electrical power line is the conductor temperature. If the actual conductor temperature is known on a real-time basis, all factors which might limit the thermal rating can be determined, such as the conductor sag, including elevated temperature creep, line hardware and splices and conductor loss of tensile strength. For this reason it is important that the actual conductor temperature on a real-time basis (i.e., as a function of time) be known.
Since load capability is normally limited by thermal rating, and since thermal rating in turn has heretofore been based on assumed pessimistic climatological conditions, it is apparent that thermal rating or load capability may be substantially increased when those pessimistic assumptions are eliminated. Thus to eliminate such assumptions and thereby substantially increase the thermal rating of the conductor, we propose to directly monitor actual conductor temperature on a real-time basis.
The surface temperature of an overhead line is dependent on four heat quantities: (a) thermal convection; (b) thermal radiation; (c) solar radiation; and (d) the internal heat generated within the conductor or I.sup.2 R losses. The first three heat quantities are a function of the physical and mechanical properties of the electrical conductor; weather conditions such as the mean wind velocity, wind direction and calmness or gustiness, ambient temperature and direct and indirect solar radiation, and the physical properties of air. The fourth heat quantity is a function of line current and conductor resistance. Conductor resistance, of course, also varies as a function of conductor temperature. Thus our invention avoids the need to measure and/or assume these heat quantities and the factors which affect them by directly measuring conductor temperature.